1. Field of the Invention
The present invention relates generally to radio transceiver systems, and more particularly to a dual mode receiver channel select filter configured for switching between Bluetooth and 802.11b wireless reception.
2. Description of the Related Art
CMOS receivers with dual-mode Bluetooth (BT) and WLAN (IEEE 802.11b) operational capabilities offer extreme flexibility for short-range wireless personal area network applications. As BT and 802.11b share the same RF frequency spectrum, they can use the same RF front-end in the receiver architecture. A low-IF receiver is suitable for BT application, as it provides a solution to de offset and flicker noise problems associated with zero-IF topology. The main drawback of a low-IF receiver is that it suffers from problems of image signals, which can sometimes be larger than the wanted signal. Complex filters provide the solution to image rejection in low-IF wireless applications. On the other hand, Zero-IF is more attractive for the reception of WLAN signals. Flicker noise does not degrade the receiver performance because of the wide bandwidth of the signal. Also, low-IF topology is expected to be power inefficient due to the relatively large bandwidth of 802.11b. Dual-mode transceivers incorporating low-IF for BT and Zero-IF (direct conversion) for 802.11b are known in the art. A typical receiver topology is where the local oscillator and the channel select filter must be programmable to accommodate both standards. Switching between the two modes is achieved by static switches.
For BT, a low-IF receiver incorporates a single conversion to an IF (in this work 3 MHz) that is a few times higher than the channel bandwidth (1 MHz). A complex filter is required for channel selection, as well as for image rejection. For WLAN mode, the signal is mixed directly to baseband, requiring separate baseband paths to maintain the negative frequency information. Highly linear I (in-phase) and Q (quadrature) identical low pass filters are needed for channel selection.
Thus, a dual mode receiver channel select filter solving the aforementioned problems is desired.